siRNA is a material which has come into the spotlight as a gene therapy since it was discovered as exhibiting an excellent effect in view of inhibiting expression of a specific gene in an animal cell. Such siRNA has been studied for the last 20 years by virtue of high activity and precise gene selectivity, and is expected as a drug, which may replace an antisense oligonucleotide (ODN) currently tried as a drug (medicine, therapy). Accordingly, more than 30 pharmaceutical companies and biotechnology companies are currently focused to develop on drug Based on the siRNA oligonucleotides (siRNA). Especially, they are developing oligonucleotide (siRNA) related therapies for treating several diseases, such as diabetes, obesity, rheumatism, Parkinson's disease, hepatitis B, hepatitis C, ADIS and cancers.
A drug which employs the conception of the oligonucleotide such as siRNA specifically break a certain specific mRNA in order to regulate an expression and metabolic process of a specific gene to suppress a transcription and protein synthesis of a target gene, thereby treating a disease. However, due to siRNA's low in vivo stability and susceptible to nuclease attack, it is easily degraded by various serum nucleases within body. Especially, for a therapy given through injection, the oligonucleotide may be degraded more fast unless chemically stably processed. Also, the oligonucleotide such as siRNA is difficult to penetrate a cell membrane having the same negative charge due to its anionic property. Consequently, the oligonucleotide may not be easily transferred into the cell, thereby causing a drastic reduction of therapy efficiency. Furthermore, the oligonucleotide such as siRNA may be identified as an external material in the living body, which may cause a side effect in an immune system. The oligonucleotide may also affect a gene present at another portion other than an originally expected gene portion, thereby causing cross-hybridization in a gene sequence.
Therefore, in order to ensure stability and minimize the side effect of the oligonucleotide (siRNA)-based drug used for disease treatment, it is required to develop drug carrier systems, such as polymeric-nanoparticles, micelles, and liposomes, which are capable of improving in vivo stability of a drug and minimize a side effect of the drug.